The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
An aircraft is powered by several turbojet engines each accommodated in a nacelle. Each nacelle also houses a set of auxiliary devices associated with the operation thereof and providing various functions when the turbojet engine is operating or stopped.
A nacelle generally has a tubular structure comprising an air inlet in front of a turbojet engine, a middle section intended to surround a turbojet fan, a rear section which may optionally include thrust reversing means and which is intended to surround the combustion chamber of the turbojet engine, and an exhaust nozzle, the outlet of which is located downstream of the turbojet engine.
Modern nacelles are often intended to house a dual-flow turbojet engine capable of generating, by means of the rotating fan blades, a flow of hot air (also called primary flow) from the combustion chamber of the turbojet engine.
A nacelle typically has an outer fixed structure called Outer Fixed Structure (OFS), which defines with a concentric inner fixed structure, called Inner Fixed Structure (IFS), including a cowl surrounding the structure of the turbojet engine itself behind the fan, an annular flow channel, also called vein, to channel a cold airflow, also called secondary flow, which circulates outside the turbojet engine.
The primary and secondary flows are ejected from the turbojet engine at the rear of the nacelle.
Each airplane propulsion set is thus formed by a nacelle and a turbojet engine, and is suspended to a fixed structure of the airplane, for example under a wing or on the fuselage, by means of a pylon or a mast fastened to the turbojet engine of the nacelle.
The rear section of the outer structure of the nacelle is commonly formed by two substantially semi-cylindrical cowls, on either side of a vertical longitudinal plane of symmetry of the nacelle, and movably mounted so as to extend between an operating position and a maintenance position which gives access to the turbojet engine.
The same applies to the middle section which is adapted to open to allow access to the fan.
It should therefore be noted that an airplane propulsion set integrates functional subsets which have relative movements and between which sealing should be handled.
More particularly, it should be noted that the rear and middle sections comprising subsets respectively used as a casing to the nozzle and a casing to the fan, the propulsion set areas playing an important role in flow generation and orientation.
In order to feed the airplane air distribution circuits (air conditioning, cabin pressurization, etc.) air is sampled at the turbojet engine compressor. This air is of course too hot and must be cooled. It is in particular cooled by a pre-cooling device (“pre-cooler”) using cold air sampled by a scoop called pre-cooler scoop.
On the other hand, the nacelle subsets are subjected to temperatures which make them expand and cause deformations, especially radial deformations.
Thus, while the interval between the fan casing and the blades of said fan must be controlled to ensure optimal efficiency of the fan, a radial expansion of the casing may result in an increase in this interval and consequently in a decrease of fan performances since more uncompressed air will escape through this clearance.
In order to overcome this drawback, the fan carter is equipped with a cold air distribution circuit to its surface called TCC “Turbine Clearance Control”. This cold air is usually sampled by a scoop located in a cold flow circulation area (vein area) called TCC scoop.
This principle also applies to other parts of the nacelle, such as the nozzle for example.
The sampling scoop is thus generally intended to ensure conveying of the air sampled to the cooling circuit.
To this end, the scoop has the form of a substantially tubular duct having a profiled sampling opening allowing to limit aerodynamic disturbances induced by the sampling.
It is inserted through a wall exposed to the cold airflow, the air sampling opening thereof leading into the circulation area of the sampled airflow. It may especially be an IFS outer panel oriented toward the circulation vein of the secondary flow.
In the case of a panel made from a metal alloy, the scoop is generally introduced into a cutout and has at its sampling opening a peripheral flange intended to ensure the aerodynamic continuity with the panel surface and the fastening of the scoop to this panel by riveting or welding.
The widespread use of composite materials in the manufacture of nacelle panels poses a major challenge to the setting of these scoops.
Indeed, at present, the structure of the scoop must be added on the panel in the same manner as for a metal alloy panel, namely by making a panel cutout substantially in the form of the scoop.
However, it is generally not advisable to make composite panel cutouts, such cutouts causing breaks in the fibers and the inner structure of the composite panel (core), which is likely to affect its integrity and mechanical resistance.
The presence of fixing means, passing through, even partially, the structure of the composite panel, is also undesirable for the same reasons.